Modern roofing materials generally represent a compromise between various performance characteristics which are highly desirable, the economics of the manufacture of the shingle itself, and limitations imposed on the roof construction process by the shingle. Most prefabricated shingles have a three or four layer structure consisting of a first asphalt layer; an intermediate support layer, such as paper, fiberglass or polyester fibers in the form of a mat or yarn; and a second, thicker asphalt layer in which is embedded weather resistant minerals such as slate or rock granules. The physical characteristics of the shingle itself vary widely depending upon the softening and the fluid ranges of the asphalt, the nature of the intermediate support, and the nature, amount and size of mineral matter contained in the upper layer. The interplay of these characteristics of the basic materials from which the shingle is constructed affect the manufacturing process and its economics.
Waterproofing materials, including shingles, are most often manufactured by a continuous manufacturing process, with the last step in the process being slicing the product as it emerges from the line into individual shingles, or convenient lengths for individual rolls. The intermediate support material serves as the basic moving framework during the manufacturing process, with hot, molten asphalt being applied to both sides thereof, and, subsequently, the weather-resistant mineral being embedded into the upper layer of hot asphalt. The moving asphalt-laden support material passes through various calendars or nip rolls to adjust the thickness of the asphalt layers and to apply pressure to embed the weather resistant mineral material. A cooling stage follows in the production line before slicing, stacking and packaging. A critical factor during manufacture is the line speed which, to a great extent, depends upon the mechanical strength of the intermediate layer support material.
The lowest cost intermediate layer support material presently used is paper. However, paper is mechanically weak and tears easily when subjected to moderate stress or elongation. In addition, paper is very notch sensitive. The paper web will tear very easily if one edge is ripped or torn and, therefore, a great deal of care must be exercised in handling the paper rolls. Thus, in the usual manufacturing process, the line speed is relatively slow when paper is used compared to stronger materials. In addition, asphalt does not adhere well to most paper supports. Also, paper is moisture sensitive, so it is usually necessary to impregnate a saturant, which is a "neat" unfilled asphalt, in the paper to get adequate adhesion and moisture resistance. Saturants are costly, offsetting the advantage due to the cheapness of the paper. Volatile components of the saturant may require expensive measures to prevent health hazards during the manufacturing process, and they may result in objectionable odor in the finished product. When subjected to cold weather, the paper layer becomes brittle as does the cold-hardened asphalt layers. If the shingle cracks due to some environmental stress, the crack may propagate from one asphalt layer, through the paper, and into the other layers, allowing water penetration.
An intermediate layer of glass fibers has some advantages over a paper layer, both in terms of shingle characteristics and the process of manufacture. However, precautions must be taken on the coating line due to the health hazard to humans which is presented by the irritating glass fibers. Shingles made with glass fibers are very brittle and tear easily, particulary in cold weather. Under these conditions, an errant hammer blow during installation of a roof could crack the shingle. Therefore, they are difficult to apply to a roof in a northern climate except during the warmer months of the year.
Fibers made from plastic materials, such as polyesters, have been used as the intermediate layer material for shingles and other roofing materials. The brittleness and low tear strength of glass and the weakness and moisture sensitivity of paper are avoided by use of these materials. However, these synthetic fibers are very expensive. In addition, these materials are subject to elongation when subjected to the stress of running through the manufacturing line and, therefore, line speeds must be reduced and production output decreased.
The use of an intermediate layer with perforations is disclosed in U.S. Pat. No. 4,565,724, where the material is fiberglass with holes in the range 50-110 mm (2-4.3 inches), and the open area amounts to 8%-14% of the lateral area of the fiber glass mat. The material was not for use in the manufacture of preformed roofing materials, as in the present invention, but rather it was intended for use in the in situ construction of a built-up roof. The contemplated in situ construction would employ a torch to melt an upper, modified bitumen layer which would then adhere to the substratum and the other layers through the large holes in the fiberglass mat. Such products are termed "button" base sheets or venting base sheets and are well known, especially in Europe.
U.S. Pat. No. 4,567,079 discloses an intermediate layer of organic, fiberglass or asbestos felt with holes, in one margin only, which comprise 1/5 to 1/2 of the area of the layer. The preferred range of diameters for the holes is 1/2 to 3/4 inch. The anticipated use of the material is again an in situ built-up construction with hot mopping of molten asphalt on the margins to obtain adherence through the perforations. Use in the construction of preformed waterproofing materials, such as shingles ,is not contemplated.